Control system and method of an injection molding apparatus of plastic materials

ABSTRACT

A system and method for controlling an actuator which actuates an axially displaceable pin valve of an apparatus for injection molding of plastic materials, where the control system includes an electronic control unit of the actuator which adjusts at least one among position, speed and acceleration of the pin valve, and a position sensor which detects a position of a plunger of the actuator and is operatively connected to the electronic control unit. The position sensor indirectly detects the position of the plunger of the actuator.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 371 National Stage of International ApplicationNo. PCT/162019/054760, filed Jun. 7, 2019, which claims priority toItalian Patent Application No. 102018000006688, filed Jun. 26, 2018. Thedisclosure of each of the above applications is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention regards apparatus for injection moulding ofplastic materials of the type comprising at least one injector providedwith a pin valve that is axially displaceable between an advancedclosing position and a receded opening position for the flow of plasticmaterial towards the cavity of a mold. Typically, the pin valve of theinjector is driven by means of an actuator which can be of the electricor fluid type.

More in particular, the invention regards the case where the actuator isof the fluid type (hydraulic or pneumatic) and specifically it regardsthe control of the actuator and, correspondingly, of the pin valve ofthe injector.

STATE OF THE ART

In the electronic control systems of the actuator of the injector, aprogrammable control unit is operatively associated to the delivery anddischarge electro-valve circuit of the actuator and it is configured toadjust at least one among the position, speed and acceleration of thepin valve. The electronic control unit is in turn operatively connectedto a position sensor which detects the position of the plunger of theactuator.

An arrangement thus made is described and illustrated for example indocument US-2015/0158227: the position sensor is physically applied tothe cylinder of the fluid actuator and thus it is capable of directlydetecting the position of the plunger.

This arrangement reveals various drawbacks.

Firstly, the need for providing the molding apparatus with specificactuators that incorporate the relative position sensors and which arerelatively expensive. Furthermore, should the sensors fail, therenormally arises the need for replacing the entire actuator.

Secondly, if planning to upgrade the molding apparatus thereof withoutelectronic control, implementing it by adding the electronic controlunit, the user should necessarily replace the fluid actuators thereofwith those provided with position sensors.

Despite the fact that documents US 2004/15295 and U.S. Pat. No.5,055,026 provide for indirectly detecting the position of the plungerof the actuator, they offer poorly effective solutions.

SUMMARY OF THE INVENTION

The object of the present invention is to overcome the aforementioneddrawbacks, and such object is primarily obtained through a system forcontrolling a fluid actuator, comprising a cylinder and a plunger whichactuates an axially displaceable pin valve of an injector in anapparatus for injection molding of plastic materials of the type definedabove, wherein the position sensor indirectly detects the position ofthe plunger of the actuator, whose peculiar characteristic lies in thefact that the position sensor is arranged at a remote position withrespect to the actuator, and more in particular it is operativelyassociated to a movable member actuated simultaneously with theactuator, for example consisting of the plunger of an auxiliary fluidjack inserted into the delivery and discharge circuit of the actuator.The position of the plunger of the auxiliary fluid jack detected by theposition sensor will thus be proportional to the stroke of the pin valveof the injector, and the signals transmitted by the position sensor tothe electronic control unit will allow to manage the position and/or thespeed and/or the acceleration of the pin valve during the injection as afunction of the programming of such electronic unit.

The control system according to the invention reveals the advantage ofbeing flexible, in that it can be adapted to any type of fluid actuatoreven previously existing in a molding apparatus. Furthermore, theposition sensor can be installed in any position—even remote—and thusmore easily accessible, such as for example on the mold, on board thepressing machine and even in a position outside the pressing machine ofthe molding apparatus. Besides making the position sensor easilyaccessible in case of failure, such positioning keeps the apparatus awayfrom high temperatures thus attaining greater reliability and precisionof the entire electronic control.

The position sensor is also advantageously suitable to manage, by meansof an electronic control unit, the stop of the actuator should the pinvalve be at an intermediate position between a full closing position anda maximum opening position, and it is also suitable to serve as anend-stop for the movement of said pin valve, as well as detect possibleleakages of the fluidic circuit of the actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to theattached drawings, provided purely by way of non-limiting example,wherein:

FIG. 1 is a diagram showing the application of the position sensoraccording to the invention to a first example of an electrical-hydrauliccircuit for the actuation of an actuator of an injector,

FIG. 2 is a diagram similar to FIG. 1 of a second example, and

FIG. 3 is a sectional schematic view of an embodiment of the positionsensor.

DETAILED DESCRIPTION OF THE INVENTION

Initially referring to FIG. 1, following is a summary description of anexample of a control system of an injector of an apparatus for injectionmolding of plastic materials, comprising—in a per se known manner (andthus not illustrated in detail)—a nozzle in which the pin valve isaxially displaceable between an advanced full closing position and areceded maximum opening position of the flow of the plastic materialfrom a hot runner to the cavity of a mold. Generally, an apparatus thusmade can for example be of the type described and illustrated in thepreviously mentioned document US-2015/0158227.

The displacement of the pin valve of the injector is obtained by meansof a fluid actuator A including a cylinder a and a plunger b whose stemc is directly or indirectly connected to the pin valve of the injector.The actuator A, pneumatic or hydraulic, is of the double-acting type andit is connected to a delivery line P and to a return line T of apressurised fluid, which mutually invert alternatingly depending on thedisplacement direction of the plunger b of the actuator and thus of thepin valve of the injector. The fluid, in the hydraulic case describedherein, is supplied and discharged by a distribution unit schematised bysection Y of the circuit, in turn connected to the delivery P anddischarge T (section Z). The section Y may take various configurations,schematically illustrated, as a function of the needs and requests ofthe user of the molding apparatus.

Arranged between the actuator A and the distribution section Y are threesections B, C and E, all connected to a programmable electronic controlunit D.

The section B includes a block solenoid valve by means of which theactuator A, and thus the pin valve of the injector, can be stopped in atleast one intermediate position between the full closing position andthe maximum opening position.

The section E includes a flow rate adjustment solenoid valve by means ofwhich it is possible to control the displacement speed of the plunger bof the actuator A, and thus the speed of the pin valve of the injector.In the example described herein, the section E allows to adjust thedisplacement of the pin valve at a single constant speed, programmableby means of the control unit D.

The section B comprises a block solenoid valve which, upon command bythe control unit D, stops the stroke of the plunger b of the actuator A,and thus the stroke of the pin valve of the injector, in at least oneintermediate position between the full closing and maximum openingpositions.

The section C, interposed in this case between the sections B and E,includes—according to the invention—a position sensor generallyindicated with S which indirectly detects the position of the plunger bof the actuator A, and thus of the pin valve of the injector.

The expression indirect is used to indicate, in the description and inthe claims that follow, the fact that the position sensor S is separatedfrom the actuator A and it can thus be arranged in a remote position andspaced from the hot runner: for example on the mold, or on board thepressing machine or even outside the pressing machine of the moldingapparatus.

As illustrated in detail in FIG. 3, the position sensor S consists of anauxiliary hydraulic circuit consisting of a cylinder 1 displaceable inwhich is a plunger 2 which delimits—in the cylinder—two chambers each ofwhich is provided with a respective inlet/outlet 3, 4 connected to thehydraulic circuit of the actuator A. A linear position transducer 5,comprising a stem 6 slidable on which is an annular displaceable contact7 carried by the plunger 2, is operatively connected to the electroniccontrol unit D for indicating the position of the plunger 2 and thus,indirectly, the position of the pin valve of the injector.

The inlets/outlets 3, 4 of the auxiliary fluid jack S are connected—asmentioned—to the hydraulic circuit of the actuator A by means of asolenoid valve provided for in the section C, also controlled by theelectronic control unit D, as outlined hereinafter.

Upon filling the hydraulic circuit, the solenoid valve of the section Cis opened by the electronic unit D to allow the fluid to enter into thetwo chambers of the auxiliary hydraulic jack S filling them with oil andemptying them of air. At the end of this step, the solenoid valve of thesection C is shut.

Subsequently carried out is a reset step, during which the actuator A isactuated to take the plunger b and thus the pin valve of the injector tothe full closing position and then to maximum opening position, so as torespectively identify the origin and the maximum of the displacement.This step offers the possibility of being able to use the same positionsensor S in molding systems provided with different actuators A.

During the normal regime operation, the hydraulic circuit oil will flowwith reciprocating motion displacing the plunger 2 of the auxiliaryhydraulic jack S proportionally to the stroke of the plunger b of theactuator A. The transducer 5 will detect the instantaneous position ofthe plunger 2 transmitting the relative signal to the electronic controlunit D which will process it and use it to manage the electric controlsof the various solenoid valves of the circuit so as to control theposition, the speed and possibly the acceleration of the pin valve ofthe injector in a programmed fashion.

The variant of the hydraulic diagram represented in FIG. 2 is analogousto the embodiment described with reference to FIG. 1 and it differs fromthe latter solely due to the fact that the section E is configured sothat the displacement speed of the pin valve adjusted by the electronicunit D can be double instead of single.

The advantages deriving from the invention, and specifically in that theposition sensor S is physically separated from the actuator A, aresummarised hereinafter:

-   -   maximum flexibility, due to the possibility of being able to        adapt to different types of actuators, of any size and        manufacturing,    -   possibility of remote-positioning and thus not affected by the        high temperatures of the hot runner of the apparatus,    -   possibility for the position sensor S to also serve as an        end-stroke for the actuator A,    -   capacity to detect and signal even possible leakages in the        fluidic circuit of the actuator A,    -   possibility of subsequently implementing, i.e. application of        the electronic control even to previously existing molding        apparatus, without having to directly intervene on the actuator        of the or of each injector.

Obviously, the construction details and the embodiments, in particularas regards the configuration of the position sensor and relativetransducer described above by way of example, may widely vary withrespect to what has been described and illustrated, without departingfrom the scope of protection of the present invention as described inthe claims that follow.

In particular, the indirect detection at a remote position could beactuated—instead of by means of the plunger of the auxiliary hydraulicjack—by a different mechanical device or device of any other nature,known to a man skilled in the art, capable of performing the samefunction.

The invention claimed is:
 1. A system for controlling an actuator whichactuates an axially displaceable pin valve of an apparatus for injectionmolding of plastic materials, wherein the actuator is a fluid jackhaving a cylinder and a plunger, said system comprising: an electroniccontrol unit of the actuator for adjusting at least one among position,speed and acceleration of the pin valve, and a position sensor fordetecting the position of the plunger of the actuator and operativelyconnected to said electronic control unit, wherein said position sensoris operatively associated to a moveable member actuated simultaneouslywith said actuator and includes a plunger of an auxiliary fluid jackinserted in a delivery and discharge circuit of the actuator and locatedat a remote position with respect to said actuator.
 2. The systemaccording to claim 1, wherein said plunger of said auxiliary fluid jackis part of a linear position transducer.
 3. The system according toclaim 1, wherein said position sensor is configured to detect and signalleakages in the delivery and discharge circuit of said actuator.
 4. Thesystem according to claim 1, wherein said position sensor also serves asan end-stroke of movement of said pin valve.
 5. An apparatus forinjection molding of plastic materials including at least one injectorprovided with an axially displaceable pin valve, an actuator whichactuates said pin valve and includes a fluid jack having a cylinder anda plunger, an electronic control unit of the actuator for adjusting onefrom among position, speed and acceleration of the pin valve of the atleast one injector, the apparatus comprising: a position sensor whichindirectly detects a position of the plunger of the actuator and isoperatively connected to said electronic unit, wherein said positionsensor is located at a remote position with respect to the actuator, andwherein said position sensor is operatively associated to a movablemember actuated simultaneously with said actuator and includes a plungerof an auxiliary fluid jack inserted in a delivery and discharge circuitof the actuator.
 6. The apparatus according to claim 5, wherein saidposition sensor comprises a linear position transducer operativelyassociated to said plunger of the auxiliary fluid jack.
 7. The apparatusaccording to claim 5, wherein said position sensor also serves as anend-stroke of movement of said pin valve.
 8. The apparatus according toclaim 5, wherein said position sensor also serves as a detector for anyleakages of a fluidic circuit of the actuator.